In recent years, ring resonators (“resonators”) have increasingly been employed as essential components in optical networks and other nanophotonic systems that are integrated with electronic devices. A resonator can ideally be configured with a resonance wavelength substantially matching a particular wavelength of light. When the resonator is positioned adjacent to a waveguide within the evanescent field of light propagating along the waveguide, the resonator evanescently couples at least a portion of the particular wavelength of light from the waveguide and traps the light for a period of time. Resonators are well-suited for use in modulators and detectors in nanophotonic systems employing wavelength division multiplexing (“WDM”). These systems transmit and receive data encoded in different wavelengths of light that can be simultaneously carried by a single optical fiber or waveguide. Resonators can be positioned at appropriate points along the optical fiber or waveguide and operated to encode information by modulating unmodulated wavelengths of light and operated to detect wavelengths of light coding information and convert the encoded wavelengths into electronic signals for processing.
However, a resonator's dimensions directly affect the resonator's resonance wavelength, which is particularly important because in typical WDM systems the wavelengths may be separated by fractions of a nanometer. Environmental factors affecting a resonator's resonance wavelength include low resonator temperatures due to low ambient temperature or lack of power dissipation of neighboring circuits. In addition, even with today's microscale fabrication technology, fabricating resonators with the dimensional precision needed to insure that the resonator's resonance wavelength matches a particular wavelength of light can be difficult. These problems arise because the resonance wavelength of a resonator is inversely related to the resonator's size. In other words, the resonance wavelength of a small resonator is more sensitive to variations in resonator size than that of a relatively larger resonator. For example, a deviation of just 10 nm in the radius of a nominally 10 μm radius resonator results in a resonance wavelength deviation of 1.55 nm from the nominal resonance wavelength for which the ring resonator was designed. This 0.1% deviation approaches the limits in accuracy for fabricating resonators using optical lithography. A deviation of this magnitude is undesirable and in fact may be unacceptable in typical optical networks and microscale optical devices where the wavelength spacing may be less than 1 nm.
Systems and methods that enable one to monitor a resonator's performance during operation and accordingly tune the resonator to correct for changing environmental effects and any manufacturing defects are desired.